glsl: Convert mix() to use a new ir_triop_lrp opcode.

Many GPUs have an instruction to do linear interpolation which is more
efficient than simply performing the algebra necessary (two multiplies,
an add, and a subtract).

Pattern matching or peepholing this is more desirable, but can be
tricky.  By using an opcode, we can at least make shaders which use the
mix() built-in get the more efficient behavior.

Currently, all consumers lower ir_triop_lrp.  Subsequent patches will
actually generate different code.

v2 [mattst88]:
   - Add LRP_TO_ARITH flag to ir_to_mesa.cpp. Will be removed in a
     subsequent patch and ir_triop_lrp translated directly.
v3 [mattst88]:
   - Move changes from the next patch to opt_algebraic.cpp to accept
     3-src operations.

Reviewed-by: Matt Turner <[email protected]>
Reviewed-by: Eric Anholt <[email protected]>
Signed-off-by: Kenneth Graunke <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/glsl/ir.cpp b/src/glsl/ir.cpp
index 4ccdc42dce0..717d6f610ef 100644
--- a/src/glsl/ir.cpp
+++ b/src/glsl/ir.cpp
@@ -416,6 +416,9 @@ ir_expression::get_num_operands(ir_expression_operation op)
    if (op <= ir_last_binop)
       return 2;
 
+   if (op <= ir_last_triop)
+      return 3;
+
    if (op == ir_quadop_vector)
       return 4;
 
@@ -502,6 +505,7 @@ static const char *const operator_strs[] = {
    "pow",
    "packHalf2x16_split",
    "ubo_load",
+   "lrp",
    "vector",
 };